Inhibition of Respiration in Prototheca zopfii by Light.

Irradiation of cells of Prototheca zopfii with blue light inhibited the respiratory capacity of the cells. The inhibition of respiration was correlated with a photodestruction of cytochrome c(551), cytochrome b(559), and cytochrome a(3). Cytochrome c(549), cytochrome b(555), and cytochrome b(564) were unaffected by the irradiation treatment. The alpha-band of reduced cytochrome a was shifted from 599 to 603 nm by irradiation, an effect similar to that observed when methanol was added to nonirradiated cells. The presence of oxygen was required during irradiation for both photoinhibition of respiration and photodestruction of the cytochromes. Cytochrome a(3) was protected against photodestruction by cyanide. Photodestruction of these same cytochromes also occurred when washed mitochondria of P. zopfii were irradiated.